In addition to the recognized detrimental affects of sunlight on printed or colored fabrics and painted surfaces, human hair damage caused by sunlight in the ultraviolet spectrum is more severe than that resulting from all other factors such as weather, wind, atmospheric pollution, salt water, chlorinated water, perming, coloring, bleaching and improperly applied or repetitive treatments. Notwithstanding the need for effective sunscreens, none have been developed which provide desired hair substantivity while avoiding other deleterious changes in structure, brittleness, hair softness and the like. Prior attempts to remedy these problems have proven unsatisfactory. For example, U.S. Pat. Nos. 3,879,443; 3,878,229; 4,069,309 and 4,680,144 disclose various sunscreens dependent on an ester functionality. However, these compounds tend to be hydrolytically unstable to the extent that the formulator must avoid conditions conducive to hydrolysis during formulation. Also, since these esters lack hydrogen bonding capability with skin protein or hair keratin, their hair substantivity is not satisfactory.
U.S. Pat. No. 4,256,664 proposes several p-substituted aromatic amines or nitro containing sunscreens having an amide functionality and optionally containing a hydroxy substituent. However, the primary amines of this patent oxidize rapidly in air, thereby altering desired hair color and, in some instances, form nitroso amines some of which are known carcinogens. Additionally, the primary amines and nitro compounds are recognized skin irritants. Further, the amine compounds are subject to intermolecular and solvent hydrogen bonding which characteristic causes a significant shift in UV maxima absorption and reduces absorption in the desired spectrum range.
M. F. Saettone et al. in THE INTERNATIONAL JOURNAL OF COSMETIC SCIENCE, Vol. 8, 9-25, 1986, describes types of amido quaternaries based on salicyclic and cinnamic acids. The salicylamides are ortho substituted with spatial arrangements permitting internal molecular hydrogen bonding. The ortho relationship of the phenolic group to the bulky amide group causes steric hindrance and stress within the molecule. To counter this steric effect, the groups which deviate slightly from planarity are present. However, any minor deviation from planarity causes a reduction in the extinction coefficient and hence a corresponding reduction in the efficacy of protection against harmful sun rays. On the other hand, cinnamoylamides have additional unsaturation and conjugation with respect to both the aromatic ring and the carbonyl group. This structure permits electron delocalization to take place within the molecule; but, although the energy corresponding to this electron transition corresponds to a desired wavelength of about 305 nm, the molar extinction coefficient is materially lower than that for the corresponding para-dimethylamino carbonyl analog. Finally, the cinnamoyl compounds are subject to cis-trans isomerization as well as to oxidative cleavage and polymerization, i.e. characteristics to be avoided for effective sunscreens.
Still another patent, U.S. Pat. No. 4,061,730, seeks to remedy the above problems by the use of quaternized benzylidene camphor sunscreens. However, since quaternization eliminates conjugation in the compound, the sun protection efficiency is significantly reduced.
From the above discussion, it will be appreciated that the discovery of a commercially viable and hair substantive sunscreen is remote.
Other heterocyclic quaternary salts of pdialkylamino benzamide derivatives which are effective substantive compounds for personal care and other commercial uses are covered in patent application Ser. No. 08/111,690, filed Aug. 25, 1993 by Ratan K. Chaudhuri et al.
It is an object of the present invention to provide an effective, non-irritating sunscreening agent which is not subject to hydrolysis, which has high substrate substantivity and which is an alternative to the compounds claimed in Ser. No. 08/111,690 [ibid].
Another object of the invention resides in the synthesis of said sunscreening agent.
Still another object is to provide a novel water insoluble sunscreening agent for extended use in hair care.
These and other objects will become apparent from the following description and disclosure.